Method and apparatus for converting heat directly to electricity



Oct. 21,1958

H IMELMANN I 2,857,446

METHOD AND APPARATUS FOR CONVERTING HEAT DIRECTLY TO ELECTRICITY Filed Sept. 1, 1953 4 Sheets-Sheet 1 INVENTOR. HENRY L. IMELMANN ATTORNEYS H. v QIMELMANN Oct, 21, 1958 2,857,446

METHOD AND APPARATUS FOR CONVERTING HEAT DIRECTLY TO- ELECTRICITY 4 Sheets-Sheet 2 Filed Sept. 1, 1953 jNVENTOR. HENRY IMELMANN ATTORNEYS Get. 21, 195% H. L. IMELMANN 2,857,446 METHOD AND APPARATUS FOR CONVERTING HEAT DIRECTLY TO ELECTRICITY Filed, Sept. 1, 1955 4 Sheets-Sheet 3 J ya a I! m u m m PW'I hum Jl -Jlmll //4 INVENTOR. "HENRY L. IMELMANN ATTORNEYS Oct. 21, 1958 Filed Sept. 1, 1953 //2 /24 FIG. I6

H. METHOD AND APPARATU L IMELMANN S FOR CONVERTING HEAT DIRECTLY TO ELECTRICITY 4 Sheets-Sheet 4 INVENTOR. HENRY L. IMELMAN N ATTORNEYS United States Patent METHOD AND APPARATUS FOR CONVER'UNG HEAT DIRECTLY TO ELECTRICITY Henry L. Imelmann, Arlington Heights, Ill., assignor to Thermo Power, Inc Franklin Park, 111., a corporatron of Illinois Application September 1, 1953, Serial No. 377,766 3 Claims. (Cl. 136-4) The present invention relates to a method and apparatus for converting heat directly to electricity by a new process which might be considered substantially the reverse of the conventional electric heating process, and, specifically, to a fuel cell defining a practical device for converting heat directly to electrical energy without the necessity of any movable or rotatable parts or the like.

Electric heating has been extensively used for many years in hundreds of applications in homes, industry and the like. Perhaps one of the best known applications is electric cooking, where upon supplying an electrical potential to the terminals of a resistance element electrical energy is converted directly to heat energy. The commonly used electrical potential is an alternating current potential, but, obviously, a direct current potential would work equally well for electric heating. I have discovered that this process of electric heating is reversible, and by applying heat to a resistance element direct conversion to electricity can be accomplished. The electrical energy obtained in this way is a direct current electrical energy. There have been, for many years, attempts to convert heat directly to. electricity which have been broadly termed thermoelectric generators, and the present invention could also be termed a thermoelectric generator, although I prefer to term it a fuel cell or resistance generator. In general, such prior thermoelectric generators have depended upon the thermoelectric effect which was discovered in the ,first quarter of the nineteenth century by Seebeck. Seebeck discovered that if the two junctions in a closed circuit defined by two dissimilar materials were maintained at diiferent temperatures, a steady electric current would flow in the closed circuit. The electromotive force causing the currents to flow in the Seebeck arrangement was found to be proportional to the temperature diflerence between the two junctions, and a function also of the materials making up the circuit commonly referred to as a thermocouple. In the years since Seebecks discovery there have been numerous attempts to generate electricity directly from heat using the thermocouple principle. However, none of these numerous attempts have been successful, and prior to the present invention no practical thermoelectric generator using the thermocouple principle has been commercially successful because of the very small currents produced and the low efiiciencies obtained. The thermocouple principle has been extensively used commercially only in the field of temperature measurement. I

It is my belief that some phases of the thermocouple principle have not been fully understood, and that, actually, there are some misconceptions which have precluded successful thermoelectric generators from having been produced. Consequently, although there is some similarity between the present invention and prior arrangements, I prefer to consider the present invention as not embodying the thermocouple principle, but as embodying the reverse of the principle involved in resistance heating. In order to provide a complete un- 2,857,446 Patented Got. 21, 1958 present invention and thermocouple generators which have been described heretofore will become apparent.

At the outset I have found that current can be generated in a resistance element by applying heat to one segment of the resistance element, and the magnitude of the current will be determined by the ohmic resistance of the resistance element. The voltage across the resistance element will be determined by the material from which the resistance element is made as well as the material of which the terminal connected to the hot end of the resistance element is made, and will also depend upon the temperature differential between the ends of the resistance element. For ideal conditions with certain configurations of the resistance element the hottest portion of the resistance clement should be the one end connected to the above-mentioned terminal, and the other terminal of the resistanceelement should be the point thereon beyond which no heat is conducted from the hottest portion thereof. It is true that when ever terminals are applied 'to such resistance element a dissimilar material enters the picture, and there is a tendency then to consider that a thermocouple exists involving the thermocouple principle. In the ensuing description numerous references to the prior art thermocouple type generators are made in order to aid in understanding the present invention, even though it is believed that applicants invention is concerned with a principle analogous to the reverse of the principle involved in the process of electric heating.

The literature is replete with articles on proposed thermoelectric. generators with varying efficiencies, some writers contending that efficiencies in excess of are possible, and others contending that 'efficiencies above 2% or 3% are not obtainable with materials presently known. The thermocouple itself upon which such prior art devices are alleged to be based is notoriously inefficient, even when operating at the highest allowable temperature difference. The conclusion generally atrived at by investigators in this field is that the problem of producing thermoelectric generators with efficiencies higher than a few percent can be solved only by finding new materials of high thermoelectric power and low specific electric resistance, or, in other words, high electric conductivity and low specific heat conductivity. Everyone working in this field heretofore has concluded that such materials presently are not available, and no practical thermoelectric generator employing the thermocouple principle has consequently been available on the market. The reasons generally given for the inefficient operation of prior thermoelectric generators of this type have been tied up with the fact that materials of low heat conductivity are usually also materials of low electrical conductivity, and, moreover, because of this, great difliculties have been encountered in maintaininga substantial difference in temperature between the so-called hot and cold junctions of such thermoelectric generators. I have discovered an arrangement using materials of the same type as in prior thermocouple generators, which, based upon a principle analogous to the reverse of electric heating, provides an eflicient generator of electricity which, for want of a better term, might be called a resistance generator.

It would be desirable, therefore, to provide a generator employing presently known materials for producing a high electric current output having an efficiency comparable with that of presently known means of generating electricity and far in excess of anything heretofore considered in the thermoelectric generator field. I have discovered that such a fuel cell or resistance generator is practical in efiiciencies greatly in excess of 2% or 3%, and, in fact, in efficiencies in excess of 50% which will produce outputs comparable from the standpoint of voltage and current with literally thousands of applications where other means of generating electricity are employed. 7 V

I In the field of thermoelectricity, Lord Kelvin, in the nineteenth century, discovered what has come to be known as the Thomson effect; He showed that if there was a temperature gradient along a metallic conductor, it was accompanied by a smallvoltage gradient whose magnitude and direction depended upon the particular metal. It is believed that in the resistance. generator in the present invention an electric currentis effectively generated in a' single resistance materialdue to the temperature gradient along this single material by heating one segment thereof. Itis true that electric terminals connected. to this single resistance material effectively provide a junction, but theseterrninals may be considered as part of the external circuit, The fact that ajunctibn is present erroneously leads one to conclude thatthe thermocouple principle "is involved, when, actually, it is not. A thermocouple always requires two junctions, a hot and a cold junction. With the presentinvention a cold junction is not required, and the material of which the other terminal is made, makes ,no difference, since it merely serves as a conductingpath. A resistance elementf'ormed of a lengthof constantan with copper terminals at each end can have its' current output greatly changed merely by changing the length or cross-sectional area of the constantan. Effectively, therefore, the constantan may be considered as the generator of the current, with the copper te'rminalsjcor'nprising part of the external circuit.

' Prior to the present invention no one was able to convert heat directly to current with a single element and obtain currents of any magnitude. In fact, there is nothing in the prior art indicating that current in'excess of several amperes, andcertainly not in excess of five amperes, were ever obtained by direct conversion of heat energy to'electricalenergy in a single cell. One of the common statements appearing in most of the literature relative to so-called thermocouple generators is to the effect that as generators of electric currents thermocouples have little use owing to their small e. m. f., and their comparatively highginternal resistance. 'The: reason for such low current-generation apparently resides in the alleged problem of keeping the cold junction cold, which problem is mentioned as being insurmountable in all the literature except at the expense-- of efficiency; Thus, the hot and cold junctions Were separated substantial distances. Obviously, the ohmic resistance of the thermocouple increases substantially as the distance between the hot and cold junctions is increased, since the ohmic-resistance of aconductor increases in 'accordance with the following well-known expression:

increased. To obtainany current output, therefore, it

was necessary to increase the cross-sectional area, which required a greatly increased massat the hotjunction to be heated. I have discovered that there is a fallacy in the heretofore accepted premise that .to maintain a tern- .perature differential between the two ends of a material such as the hot and cold junctions of a thermocouple they must be spaced a substantial distance. apart. I

have found that constantan in short lengths of less than an inch and of small diameter can have one end heated to 1500 F., and the other end will remain at room temperature. Thus, by using hort lengths of material, the current flowing in a resistance element is greatly increased. I have been able with a single resistance element, solely by maintaining a temperature gradient along said element, to produce currents of the order of one hundred amperes with a relatively high voltage based on a substantial temperature gradient as well as on the particular materials employed.

It can be shown that if a short length of resistance material is provided with a substantial restriction in cross-sectional area for but a very small fraction of the length thereof, a substantial temperature differential can be maintained between the ends of the material without affecting the over-all electrical resistance, which will remain substantially unchanged. In other words, the thermal conductivity-through this material will'be greatly decreased. A great reduction in 'cross sectional area, even though infinitely short, will greatly decrease thermal conductivity, but if v'eryshort will have little elfect on electrical conductivity, since the over-all resistance of an electrical conductor is equal to the sum of the resistances of successive lengths thereof. Thus, if there is included a section of verysmall cross section but infinitely short, it will have little effect on the over-all re- 'sistance.- Although in prior art thermoelectric generator disclosures the use of restrictions to reduce thermal conductivity was suggested, these restrictions were of such length as to greatly impair electrical conductivity and, hence, reduce current output to an impractically low value for power purposes. It would be desirable toemploy this feature to provide a grea tly increased current output from a single thermocouple element.

It will be appreciated that there are numerous applications requiring a source of energy which .are presently supplied from internal combustion engines or, similar means which are notoriously inefiicient andhave numerous disadvantages with respect to noise, moying parts and the like. It would be desirable to provide an arrangement for generating electricity useful for numerous power applications in which a source of heat such as might be obtained fromnatural ormanufactured gas. or burning fuel of any nature can be converted directly to electricity which can be used in the conventional manner. I

Accordingly, itis an object of the present inventionto provide an improved process of converting heat directly to electricity with great efficiency. 7

It is another object of the present invention ,to provide .improved apparatus for converting heat directly to electricalenergy without the requirement of any movable parts, andwherein such conversion will be accomplished at an efficiency comparable with or in excess of the efliciencies of conventional prime movers such as internal combustion engines and the like.

It is another objectof the present invention to provide a greatly improved and practical resistance generator .with means for maintaining a substantial differential of temperature between the two ends of the resistance element of the apparatus without expending any power other than that required to heat a small portion thereof.

It is a further object of the present invention to provide ,a fuel cell which involvesapplying heat to a resistor element including means for restricting the thermal con- ,ductivity of the resistor element without substantially impairing the electrical conductivity.

It is stillanother object of the present invention to proyide in a fuel cell employing "a resistor, to a portion of which heatis applied, -utilizing a configuration of the resistor whereinthe electrical resistance is independent of length thereof while the heat conductivity between two portions of said resistor can be reduced to any desired minimumby increasing the lengththereof.

-- t-A nother object of the present invention. residesin an element currents in excess of five amperes can readily be obtained with no problem of maintaining a temperature differential between two different portions of said element.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the present invention reference may be had to the. accompanying drawings in g which:

Fig. 1 is a perspective view of a simple embodiment of the present invention;

Fig. 2 is a perspective view illustrating another embodiment or the present invention;

Fig. 3 is a top plan view, partly in section, of Fig. 2, assuming that the apparatus of Fig. 2 comprises only a single generator element rather than several connected in series;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 3;

Fig. 5 is an enlarged sectional view of a portion of Fig. 2 taken substantially on line 5-5 of Fig. 2;

Fig. 6 is a somewhat schematic view of an arrangement to aid in understanding the embodiment of Fig. 2;

Fig. 7 is a perspective view illustrating another embodiment of the present invention;

Fig. 8 is an end view of a shown in Fig. 7;

Fig. 9 is a greatly enlarged sectional view taken on line 9-9 of Fig. 7;

Fig. 10 is another greatly enlarged sectional view taken on line 10-10 of Fig. 7;

Fig. 11 is a plan view of one lamination of the device of Fig. 7; V

Fig. 12 is a plan view ofinsulating members utilized in the arrangement shown in Fig. 7;

Fig. 13 is a perspective view of another modification of the present invention;

Fig. 14 is a side elevational view, partly in section, of Fig. 13 with the portion in section taken substantially on line 14-14 of Fig. 15;

Fig; 15 is a sectional view taken on line 15-15 of Fig. 14, assuming that Fig. 14 shows the complete structure;

Fig. 16 is a top plan view, partly in section, of a portion of Fig. 13;

Fig. 17 is a sectional view taken on line 17-17 of Fig. 16, assuming that Fig. 16 shows the complete structure; Fig. 18 is a greatly enlarged perspective view of a portion of Fig. 13;

Fig. 19 is a greatly enlarged perspective view of another portion of Fig. 13; and

Fig. 20 is a somewhat schematic view of a modification of Fig. 2. V

The present invention is primarily concerned with an arrangement in which a resistance element is connected in an electric circuit and means are provided to heat a portion of said resistance element to maintain a temperature differential between different portions thereof whereby a potential difference will exist causing a current to flow in said electric circuit. Means are provided for maintaining only a minimum portion of the resistance element at a high temperature sufiicient to set up the voltage. It will be understood that as far as the present invention is concerned the resistance material may comprise constantan, iron, Chromel, or numerous other materials, preferably resistance materials which are outside the so-called precious metal class.

It is recognized that only a veryfew types of thermoelectric generators have reached the production stage.

portion of the apparatus exploded perspective The best known commercially produced apparatus is Giilchers gas heated thermoelectric generator with an over-all efiiciency of one-half of 1%., The early efforts at making thermoelectric generators have been summarized in book form by Peters, in 1908, in Thermoelemente und Thermos'alulen. Essentially, the fuel cell or resistance generator of the present invention consists of a single resistance element or a number of elements which are identical except perhaps for the material of which they'are made. The thermal efficiency is not influenced by the number of elements involved, and it is possible to combine such resistanceelements in series and parallel to obtain the desired currents and voltages. Preferably, it is desirable to determine'the necessary output current and design single elements producing this current, and then combine them in series to obtain the desired output voltage. It is also preferable that the physical properties of the materials employed do not change during operation. The resistance generator requires terminals at the ends of the resistance material generally formed of copper. Thus, there are provided two dissimilar materials, i. e., the resistor material and one of the copper leads or terminals, thereby effectively defining the hot junction of thermocouple terminology. The hot junction requires welding or copper brazing or the like, and it should be free of any additional electrical resistance, since from the following discussion it will be apparent that maintaining the electrical resistance of the fuel cell at a minimum is essential. It will be apparent at once that the hot junction cannot be operated above a certain temperature limited by the melting points of the materials making up the fuel cell. Heretofore it has been established that because of the irreversible heat conduction occurring in any material, a considerable amount of heat is conducted away from the hot junction, and it was felt that this energy had to be removed by suitablecooling. I have discovered, however, that in all mate-- rials there is a point along the length thereof beyond.

a flame or other heat source to raise the temperature there-- of substantially. It will be found that under these conditions the other end of this material will remain at a relatively low constant temperature with no external cooling required. I have, moreover, discovered an arrangement for obtaining a minimum electrical resistance while permitting at the same time any desired distance between the hot and cold portions of the resistance element, and, consequently, insuring any desired temperature differential limited only by the materials involved.

Referring now to Fig. 1 of the drawings, there is illustrated one embodiment of the present invention which might be termed a very simple fuel cell or resistance generator, designated generally by the reference numeral 22. As illustrated, this fuel cell comprises, a resistance element generally designated by the reference numeral 23, and comprising three sections: a first short section 23a of one cross-sectional area, a very short section 23b of a very small cross-sectional'area, and a third and longer section 23c of the same cross-sectional area as 23a. The

resistance material 23 might comprise constantan, Chromel, iron, ciated with thermoelectricity. Connected to the ends of the resistance element 23 are a pair of terminals 24 and 25, respectively. These terminals are preferably copper, which is a conventional terminal material. It Will be apparent that there is, therefore, provided between the end of the resistance material 23 comprising the section 23a and the terminal 24 a junction which may be termed a hot junction, and is designated in Fig. 1 of the drawings by the reference numeral 26. Preferably, the terminal 24 is welded, copper brazed or otherwise suitably secured to the resistance element 23 to define the hot junction 26, while the terminal 25 may be connected by or any of the materials commonly assoany suitable means suclras silversolde'r or the like 'with" theelement 23. A load 'circuit,"g"enerally designated as 27, is illustrated as being connected across theterminals 24 and 25-. A suitable source of heat forheating a portion of the resistance conductor 23 is schematically illus trated as a burner 28,-having the flame 29 engaging'the resistance element 23 at a point adjacent the hot junction 26.

The fuel cell 22 is so termed-because it'convertsa combustible fuel and the heat energy contained therein to electricity and, hence, based upon-the analogy of the dry cell,

the-term-fuel cell-is-applie'd' to the apparatus shown in Fig. 1' of the drawings."

It will be apparent that the portion-23b of theresistance conductor 23 defines arestricti'on or notch 30in the ele-" meat 23; In accordance with the presentinvention, this restriction or notch 30 is of very'short'length, preferably of the order'of several thousandths of an inch, and notin excess of ten-thousandths of an inch: If the resistance 23 is'constantan and the portion of the resistance element 23 at the junction 26 is heated to aternperature of 1500 F. while the otherend of the" resistanceelement '23 re-- 14 constantan wire, which'has-a diameter of .064 inch and a resistance of .006ohm' per inch, a current of ten amperes will flow if the conductor length is one inch, assuming the load impedance is negligible, and further assuming that the section 2311 adds a negligible resistance, as will be shown hereinafter; -If theresistance element 23 were reduced to one-half inch in length, theoretically the current would be doubled. Obviously, with a resistance element of larger diameter the current theoreticallycan be greatly increased;

It will be appreciatedthat the notch or restriction 30 clearly decreases thermal conductivity between the two terminals of the fuel cell 22 and has very littleeffect on the electrical resistance. For example, if the section 23b were reduced to a diameter of .032 inch, which would be the equivalent of a No. wire, its resistance, if made of constantanywould be.024 ohm per inch. If the length of the portion '23b were five-thousandthsof an inch, the resistance of that section would-be 00912 ohm; Obviously, if thislowresistance is addedto the resistance of "the rema-indertof resistance-element 23, which for a one-inch length would have a'resistance of .006 ohm, the increasein resistance would benegligible. However, since the-cross-sectional area'has been-reduced by a quarter, the conductivity of. heatfrom: the terminal 24 of the fuel cell 22 to the terminalt25 .is reduced fourfold. Thus, it will be apparent that withla simple fuel cell 22, a very high direct. current can be obtained by directly converting heat-to electricity without the requirement of any moving parts or the like. The fuel. cell of Fig. 2 is very analogous to other well-known cells such as the dry cell, the storage battery and the like. Like the dry cell, for example, the voltage output is a function of the materials employed in the cell. As was stated above, the presence of a terminal of a difierent material is essential to set up the voltage, and the current'is generated in the resistance element 23, the magnitude of which resistancewill determine the magnitude of the current which will flow.

Although. there hasbeen illustrated the provision of a restriction 30,- it will be apparent that the inherent resistance of the material from which theresistance element: 23is made to heat flow or .thermal .conductionmay be I sufiicient so that .therestriction, 30 may be dispensed with. i a

As was pointed out above,"many writers have recog nized insofarfas thermocouple generators are-concerned,' that if a'material were-available which 'was'a poor heat conductor but a good conductor of electricity, and which wasalsolcapabl'efof use to produce a voltage by virtue of the thermoelectric effect, that an efficient thermoelectric generator 'could be produced. Every writer, however, has also recognized that no such material was availfor example; can-be shown to have an ohmic resistance item the center of thedisk to the outer periphery which is independent of the diameter'but dependent solely on the resistivity of the material and the thicknessof the disk. This is alsosubstantiallytrue for a rectangular sheet of material insofar as the resistance from a pointat the center of the material to a point at the outer periphery is-concerned, If the resistance from the center to the periphery of acircular disk is independent of the diameter, then it will immediately be apparent that a desired low resistance. can be obtained by proper choice of material and thickness thereof, and at the same time by providing the hot and cold terminals, respectively, at the center and the extremity of the disk, the effective low heat conductivity between these terminals can readily beobtained by producing sufficient space between the center of the disk and periphery, or, in other words; by

increasing the disk diameter. Obviously, restrictions may also be employed to reduce thermal conductivity without substantially impairing electrical conductivity. Effectively, therefore, it will be appreciated that there has been provided a configuration of material which'is capable of having a very low resistance andyet wherein, withoutaffecting the resistance, the heat conductivity from the center to the periphery can be controlled merely by increasing or decreasing the distance between the center and the periphery. In Figs. 2 to 5 there has been il-- lustrated what might, for certain applications where very high currents are necessary, be considered the preferred embodiment of the present invention. As illustrated in Fig. 2, a fuel cell 32 is described comprising a series of substantially complete disks 33, each including a resist-- ance element arranged in a vertical stack. To distinguish the individual disks, each of which is illustrated as being substantially identical in-shape, they are designated in Figs. 2 and 5 by the same reference numeral but with a different subscript. Thus, in Fig. 2 there are illustrated a plurality of disks 33a, 33b, 33c, 33d, etc.,

disposed in Spaced parallel relationship. The construction of an individual disk is best shown in Figs. 3 and 4. Each disk comprises one terminal in the form of an annular center section 34 of a good conductor such as copper. In the event the fuel cell comprises a single disk, the section 34 will have an integral extension 35 defining a terminal connecting portion. In a stack comprising a plurality of disks 33 as shown in Fig. 2, at least one disk 33 will have a terminal connecting portion 35. The annular terminal member 34- is preferably of small diameter sufficient only to permit a suitable conduit 36 or source of fuel or other combustible material to extend through the central opening 37 thereof.

In accordance with the present invention, each disk 33 is effectively a fuel cell having a main resistance portion 38 of constantan, Chromel, or any other suitable resist- To provide the other terminal of the fuel cell defined by each plate 33, there is provided a conductor '40 around. a

the periphery "of the portion 38 and 'suitablyjoined thereto to define a circular junction 41. The terminal portions 34 and 40 and the main resistance portion 38 of each disk 33 are preferably defined in a single plane, as shown in Fig. 4, and may be manufactured as suitable stampings. The portions 34 and 38 are preferably brazed to define the hot junction 39, while the portions 38 and 40 are silver soldered or otherwise suitably electrically connected to define the junction 41.

As illustrated in the drawings, disks 33 are each provided with a segmental notch 43 to accommodate the terminal connecting portion 35 if it is to be brought out in the plane of the disk. It will be apparent, however, that where a stack of disks are employed such as in Fig. 2 where the resistance portion 38 of alternate disks is of difierent material, as described hereinafter, the terminals 35 are not necessary and preferably complete circular disks will be employed. In fact even the end disk having terminal'35 can be a circular disk if the terminal 35 neednot be in the plane of the disk. Where a single disk is employed, as shown in Fig. 4 of the drawings, a suitable terminal connecting portion 44 will be connected to the terminal or peripheral conductor 40, and a suitable load circuit can be connected across the conductors 35 and 44. Where a stack of disks 33 are employed as in Fig. 2, the conductor 44 is connected to the disk at the opposite end of the stack from the disk having the terminal 35. I

For the purpose of heating a portion of the resistance element 38 of each disk 33 adjacent the annular terminal 34, the conduit 36 referred to above is provided which may have suitable orifices or elongated slots 45 to supply a flame and heat to the annular portions 34 and, hence, the inner peripheries of the resistance elements 38. The conduit 36 may be connected to a source of fuel through suitable control means, as described in connection with other embodiments of the present invention.

Considering the single disk 33 of Figs. 3 and 4, it can be shown that the resistance between the terminals 34 and 40 can be made very, very low by choosing the proper thickness of the disk 33. At the same the heat conductivity from the inner periphery to the outer periphery of the resistance element 38 can be maintained at any value by merely increasing thespacing therebetween or, in other words, increasing the diameter of the disk 33. Obviously, if the disk is made of a very large diameter, no temperature change will occur at the cold junction 41 by virtue of any temperature increase at the hot junction 39. I have found, as a practical matter, that with relatively small diameters of the disk 33 of the order of three or four inches, the hot junction 39 may be maintained at 1500 F., for example, and the cold junction 41 will remain at room temperature.

Suitable restrictions in the form of narrow slits 47 may be provided in the plates 33 in the portion 38 closely adjacent to the'hot junction 39. These slits 47 may be obtained merely by piercing the plate without removing any material therefrom. They will greatly reduce thermal conductivity and, hence, permit using disks 33 of very small diameter.

The fact that a circular disk'will have a resistance from the center to the periphery thereof which is independent of the diameter of the disk can readily be proved mathematically. It will be noted that for a constant disk thickness as the length of the current path is increased, which is accomplished by increasing the diameter of the disk, the effective cross-sectional area of the current path is also increased. Both of these parameters appear in the resistance equation set forth above and with a disk of constant thickness they both appear as a first power, one directly and the other inversely. Thus, they neutralize each other so that resistance is independent of diameter. Withthe, arrangement in Figs. 3 and 4, therefore, a very high current can be obtained with a single element such as is shown inFig. 3, and by connecting a large number of elements in series the de-' sired voltage may be obtained.

The disks 33 may be connected in series in several difthen the arrangement of Fig. 20 for connecting them in series must be utilized. In Figs. 2 and 5 it is assumed that disks 33a, 330, etc., have the portions 38 thereof formed of constantan, while the disks 33b, 33a, etc.,

have the portions 38 thereof formed of Chromel. These particular materials have such characteristics as to cause current flow in opposite directions when the hot junctions 39 are subjected to heating. Obviously, any other two materials having this opposite characteristic may be employed instead of Chromel and constantan, which are cited by way of example only. On the assumption that alternate disks 33 of Figs. 2 and 5 are formed of different resistance materials, it may be observed that the corresponding terminals of two adjacent disks or plates 33 will be insulated from each other, while the other corresponding terminals are electrically interconnected thereby to connect adjacentplates in series to produce increased voltage output depending upon-the number of plates or disks 33 connected in series. As illustrated, alternate adjacent terminals 34- are electrically interconnected and the other alternate adjacent terminals 34 are insulated from each other. Likewise, the peripheral terminals 40 are alternately interconnected and insulated from each other. This is best shown'in Fig. 5, where it may be observed that between plates 33a and 33b the terminals 34 are insulated from each other by an insulating spacer 48. Between these same plates, however, the terminals 40 are electrically interconnected, as by the conducting spacer 49. On the other hand, a conducting spacer 50 is interposed between the terminals 34 of the plates 33b and 33c. Between these same plates 33b and 330 there is provided an insulating spacer 51 to insulate the terminals 40 thereof. In this manner successive disks or plates 33 are connected in series, and a terminal connecting portion such as 44 will be connected to the bottom disk in the stack of disks of Fig. 2. It will readily be appreciated that complete disks can be employed with even greater advantages than the notched disks illustrated.

Where the disks 33 are all formed of one material so that current fiow in all disks is in one direction, either from the terminal 34 to the terminal 40, or vice versa, the arrangement of Fig. 20 for connecting the disks in series may be employed. As there illustrated, the terminal 40 of disk 33a is connected to the terminal 35 of disk 33b, the terminal 40 of disk 33b is connected to the terminal 35 of the disk 33c, while the terminal 35 of disk 330 is connected to the terminal 40 of the disk 33d, etc. The terminal 35 of disk 33a then becomes one terminal of the series connected fuel cells, and the terminal 40 of the last of the stack of fuel cells becomes the .other terminal. It should be understood that Fig. 20

is a schematic representation, and the illustrated connections between disks would be short low resistance connections in an actual installation.

It may be appreciated that, effectively, adisk such as 33 comprises a very large number of individual resistance elements connected in parallel, and this can best be appreciated by an examination of Fig. 6 of the drawings where a plurality of resistance elements 55a, 55b, 55c, 55d, 55e, 55f, 55g, 55h, 55i, 55 55k, 55m, and 5511 are connected in parallel and are all arranged with their common ends connected to an annular terminal 34 to define a plurality of hot junctions 56 disposed around the peripheryv of a tubular member 57 having a plurality of orifices 58 so that a flame may be directed to heat the terminal-34,= and, hence,theadjacent'endsof the resistance elements 55. The'endsof the resistance ele-' ments SSremote from the-terminal34 are indicated'as being connected to an annular conductor or terminal 59 which-is suitably connected to a conductor 60; A con ductor-61 is illustrated as connected to'the terminal-34,

and a load'circuit 62 is connected to COHdUCtOISfii) and. 61. I As thenumber-of resistance elements-inthe-arrangemerit shown in Fig. 6' is increased, one will eventually f arrive at a complete circular disk with the maximumcurrent rating.-

The operation of the'arrangement shown in Figs; 2 to will readily be understood in view of the detailed de-- scription included above. It will, moreover, be apparent that-there -has-been-provided an arrangement-in which maximum'current is obtainable with a very simple configuration. The advantages of the present invention are obtainable'even'though only-aportion of a'- circular disk is employed, and it will'be appreciated that'the-resistance elementof Fig-.- 1 is'efiectively a'portion of the'disk resistance element'of Fig; 3'. 'One'can obtain some of the substantial'benefitsjof the present invention by employing only a small segment of the disk 33:. It will, further-1 more, be appreciatedfrom-the above discussion that thedesirable characteristics-of thearrangement of Fig; '2'

are to some extent carried over into arrangements such as that shown in Fig. 1 where instead of a disk or segment of a disk only conductive wires are employed.

is heated.

In certain-applications of the present invention where maximum current is not a factor, numerous other designs of the fuel cell are available. In Figs. 7 to 12 of the drawings there is disclosed an arrangement which permits excellent heat control and which does not require a terminal connection at the hot end of the resistance element.

Referring now to Figs. 7 to 12 of the drawings, thereis illustrated in Fig. 7 a generator designated by the reference numeral 7h. This generator 70 is illustrated as comprising a substantial number of identical units, each comprising two resistance elements joined together to detime a hot junction. These elements are specifically illus trated' as laminations 71 of somewhat symmetrical ccnfiguration, each lamination comprising a section or cell 71a of one material, and a section or cell 71b of a different'material, united as by copper brazing or the like at a: junction .72; By using two different'resistance materials foreach lamination with current flow inopposite directions in eachlsection relative to the hot junction, it

is readily. possible to connect a plurality of laminations 71,:each of which really comprises two cells, in series in the manner of Figs. 2 and 5 of the drawings contrasted with the arrangement of Fig. 20. As illustrated, these laminations are of somewhat U-shapedconfiguration with the junction 72.occurring at the bight of the U. The elements 71 can be defined as laminations, since in a manufacturing operation they would be manufactured as laminations by .a suitable punching operation or the like..;Preferably, the laminations have a. configuration bestshown in Figs. 7 and 8 of the drawings, in which the section 71a terminates in a narrow neck portion 73 atone end thereof, which narrow neck portion is connected'to a semicircular disk 74. Similarly, the other end terminates in a restricted area portion 75 terminatingin a. small disk portion 76. The section 71b has a similar .neck portion 77 of restricted cross section integrally connected with a semicircular disk 78. The semi circular disk portions 74 and 78 when Welded or brazed together form a circular disk having the junction 72 at the united edges thereof. The other end of the section '71bis connected by anarrow neckp'ortion 79 with the disk.8l,'the'neckportions75 and 79 being identical, and

12 the diskportions'76 3.116;808180 being identical; It will be appreciatedthat if-heat is applied to the junction 72, a potential will appear across the-terminals-76 and 80, and if connected to an electrical circuit a currentwill flow. The potential at the disks'76 and 80 will be dependent upon the temperature diiierential between the junction 72 and the terminals 76 and 89, and will also be a functionof the particular materials of which-the'sections 71a and 71b are formed. The direction of current flow will, of course; be dependent upon what the materials of section 71a and 71b comprise, but, in any'event, it will bea direct current. The laminations 71 are formed to define a central opening 81 to accommodate a suitable heat' source generally designated by the reference numeral 82. it will be'understood that the source of heatcould be quite varied. For example, electrical heating might be employed for heating the junction 72. Obviously, in a practical application, electrical heating willnot be employed, since if a'source of electrical energy is available, there-would be no point in converting it to heat and then back to electrical energy. In a practical application the source of heat 82 might generally comprise some sort of fuel or combustible material. In the simplest application, it might comprise natural or artificial gas, orit might be a gasoline or kerosene jet. If gasoline is employed as the fuelya suitable gas generator, notshown, will be incorporated in the generator; In a large power plant,'it might-comprise other burning fuel such as coal or the like; As specifically illustrated in the drawings, the source'of 'h'eat'BZ has-been shown as a tubular conduit designated by the-reference numeral 33 in Fig. 10 of the drawings; which 'isconnected through a suitable valve 84fwith a' sourceof gas or other suitable fuel supplied thereto by 'c0nduit'85. 'As illustrated, the tube 83 is provided with a plurality of orifices 87, on'e positioned immediately'adjacent the hot junction 72 of each of the laminations 71 employed in the apparatus '71 ifthe apparatus 7t) embodies one hundred laminations, then preferably the tube 83 will have one hundred orifices, each positioned immediately adjacent the corresponding junction" 72. If the laminations are relatively thin, as describedhereinafter, the plurality of orifices might com-. prise anelongated slot; "As illustrated inthedrawingsr" the conduit-8-3 is of circularcross section; It should be understood that any other cross section, and perhaps a cross section conforming to the opening designated by the reference'numeral 81 between the. sections 710. and 71b ofthe laminations 70 maybe employed Suitable insula-.-.l tion 91is provided. betweenathe' conduit 83 and the larni-m:

nations :71.

It willbe understood thatzeach lamination 71, which is effectively two cells, comprises a source of electrical energy having a predetermined voltage determined by the temperature differentialbetween the hot junction 72 and theends 76 and 80, and the materials of which the sections 71a and 71b are formed. The current fiow will depend, of course, on Ohms law, which means that the lower the resistance of this electrical circuit the higher the current that will flow. The voltage obtainable at the. terminals of each resistance is indepen'dentof the distance between -the hot junction and the terminals. Obviously, the shorter the length of the materials involved the lower the resistance. For the purpose of increasing the output voltage, a plurality of laminations such' as 71 may be connected in series, thus permitting the building up of any desired voltage. The laminations 71 are admirablyi..suited for this type of arrangement, and, as illustrated, a plurality of laminations 71 are stacked with interposed insulating laminations 92 p of the configuration shown in Fig. 12 of the drawings. As illustrated, a pair of insulating laminations 92 are shaped somewhat like one of the'laminations 71 already described, except that'semicircular or partial extensions 92a are provided at the ends of the insulating laminations adjacent the circulardisks such as 76 or 80 of the lamiand 76 are insulated from each other.

present invention, the laminations 71 had external dimensions of the order'of one inch by one inch, and a thickness of fifteen-thousandths of an inch, while the insulating laminations 92' were formed of mica and had a thickness of one-thousandth of an inch. In this embodiment the sections 71a and 71b comprised, respectively, Chromel and constantan. To complete the electrical circuit between the lamintions 71, the disks 76, and designated specifically as 76a, 76b, 76c, 76d, 76e, 76 and 76g, in Fig. 9 of the drawings, are alternately connected and insulated from each other. Asillustrated, disks 76a and'76b are insulated from each other. Disks 76b and 760, however, are electrically interconnected by a suit- 7 able means such as silver solder, designated as 96a in Fig. 9 of the drawings. A similar electrical connection 96b'is interposed betweendisks 76d and'76e. Likewise,

a similar electrical connection 960 is interposed between disks 76 and 76g. The disks 80 have been designated in Fig. 9 by the same subscripts as the disks 76 immedi- Althoughthe disks 76a and 76b ately opposite thereto. are electrically insulated from each other, the disks 80a and 80b are electrically interconnected by a suitable means 96d. Similarly, disks 80c and 80d are electrically interconnected by the means 96e, although the opposite disks 76c and 76d are insulated from each other. Likewise, also, disks 80e and 80 are electrically interconnected by means 96] even though the opposite disks 762 Similarly, disks 80g and 80h are-electrically interconnected by means each other. Preferably, the electrical interconnection which might be called the cold junction may be a silver solder connection which can readily be accomplished in the space defined between the disks 76 and between the disks 80 not filled with the insulation92. This is by virtue of the fact that the extensions 92a do not completely fill the-space defined between the disks 76 and between the disks 80. This can readily be observedfrom Figs. 9 and 10 of the drawings. With this arrangement it will be apparent that one terminal of the fuel cell may be defined by the conductor 99 connected to the disk 76a, and the otherterminal 100is connected to the particular disk 80 at the opposite end of the stack of laminations 70. The electrical circuit will then proceed from the terminal 99 through the section 71a of the first lamination, through the hot junction 72 of the first lamination, through the section 71b of the first lamination, through the electrical interconnection such as silver solder 96d'to the second lamination, and around the second lamination back to the disk 76b, through the silver solder connection 96a to t the third. lamination, and successively back and forth through the laminations 71 until the terminal 100 is reached. The potential across the terminals 99 and 100 will be the sum of the potentials, across the individual laminations. If a potential of fifty millivolts appears across the disks 76 and 80 of each lamination when a predetermined temperature differential exists between the hot junction 72 and these terminals, then, obviously, a hundred laminations in the fuel cell 70 will produce an output voltage across the terminals 99 and 100 of five volts.

For the purpose of securing the laminations 71 and the insulating laminations 92 in a unitary stack, the laminations 71 are preferably provided with openings 101, and the laminations 92 are provided with openings 102, which openings 101 and 102 are aligned to receive suit- 96g, and the opposite disks 76g and 76h are insulated from i 14 able fastening means 103, which, obviously, must insulated from the laminations 71.

One of the important features of the present invention resides in the restricted cross section of the laminations 71, particularly the restricted cross sections 73 and 77, although also including the restricted cross sections 75 and 79. It will be appreciated that such restricted cross section will greatly reduce the thermal conductivity of V the laminations 71, and, hence, will tend to prevent heat from being conducted away from the hot junction 72. It i will, moreover, be appreciated that the restricted crosssectional area at the portions 73, 77, 75 and 79 is such as not etfectively to introduced any electrical resistance as far as the currents produced by-the laminations 71 or p the thermoelectric generator 70 are concerned, this for.

the same reason as discussed in detail in connection with Fig. 1 of the drawings. I The restrictions in the cross sectional area may take various forms quite different.

from those illustrated.

Another important feature of the arrangement shown in Figs. 7 to 12 of the drawings resides in the chimney effect produced between the laminations '71- at the junctions 72. This is accomplished by virtue of the fact that the insulating laminations 92 are discontinuous at the portion thereof corresponding to the semicircular disk portions 74 and 78 so that a space is'defined betweenv adjacent disks including the junctions 72, and this space 1 acts as a chimney for combustible materials providing a heat source for the junctions 72. Maximum efliciency a of the heat source is thus obtainable, and, moreover, the junctions 72 can be heated in a manner so as to heat a minimum portion of the junction. Preferably, the junction may be heated to a temperature of the order of single lamination is preferably designed to give the desired current output. It will, moreover, be appreciated that a very small compact unit is involved, since, for

example, a five-volt fifteen ampere unit can be confined 1 in an area of the order of one inch by one inch by three inches.

In view of the detailed description included above, the operation of the generator disclosed in Figs. 7 to 12 of the drawings will readily be appreciated.

In Figs. 13 to 19 of the drawings there is illustrated a modification of the present invention quite similar to the fuel cell of Figs. 7 to '12 of the drawings. As illustrated in Fig. 13, there is provided a generator which comprises a tubular conduit 111 having a plurality of orifices 112 therein quite similar to the conduit 83 of the preceding embodiment. This conduit 111 serves as a source of heat and is connected to a source of natural gas or other fuel supplied thereto by a conduit 114 to a suitable 1 control valve 115. Mounted adjacent the conduit 111 is a suitable insulating support 117, which might be a sheet of asbestos board or similar material held in spaced parallel relationship with respect to the conduit 111 by any suitable means. As illustrated, the insulating support 117 is mounted on suitable standards 118, one disposed at each end of the support 117. The support 117 is provided with a plurality of spaced openings 120, one disposed slightly above each of the orifices 112, so that each orifice 112 has associated therewith a corresponding opening 120 in the insulating support 117. Protrudmg through the openings 120 in the insulating support 117 are the adjacent joined ends of two dissimilar resistance materials specifically 'desi'gnated as elongated elements 122 and above a corresponding orifice 112'. The'junction 124may be definedas a'hot junction; and'the dissimilar resistance materials 122 and 123 might be Chromel and constantan, as'in Figs. mo 12 of the drawings, or any other combination "of-materials capable of producing a thermal electromotive forcez Thedissimilar materials 122 and 123 joinedto form a'hot-jun'ction-124 effectively define a fuel cell-hereinaftergenerally referred to as element 125. In Fig 13a large'number ofthese elements 125 are illustrated as being connectedin series by having one arm of one element l25"connected to the *adjacenta-rm of an adjacent element 1125 thereby defining a'cold junction 126, bestshown' in-Fig: -18 of the drawings; The electrical interconnections between adjacent" elements 125 preferably comprise silver solder or similar material. The number of 'elements 125 connected in" series 'isdetermined by the-desired outputvoltage, and, as illustrated in Fig. 13, a suitable load circuit 128 is .connected'across the. end

terminals of the two endelementsrlZS. If desired, suit-- ablerestrictions of the cross-sectional area of the element 125,'whichwill adversely affect 'the'heat conductivity but notsubstantiallyaifectthe electricalconductivity as described above, may be provided." With this arrangement the'desired current output "from each element 125' and fromthe fuel c'ell110 may readilybe obtained.-

Frorn-theabove-description it=will be apparent that there has been provided an improved process of generat-' ing electricitydirectly 'fromheat by =means of a fuel cell whiclfmay have numerous applications and which can be produced-commercially to have an efficiency comparable with or in excess of presently usedmeansfor generating electrical energyyaud; moreover,which can" be confined in a'very small space. It is believed thatthe present fuel cell or resistancelgenerator can and will displace prime movers suchas are presently employed on-lawn mowers,v

power boats and the: like.

Although the correct explanations for the operation and underlying theory of the fuel cells described above are believed to have been set forth, it should be understood that these explanations. and theory are enunciated to facilitate an understanding of the operation of applicants new'process and apparatus, and are not to be construed as limitations of the invention disclosed therein.

While'there have been illustrated anddesc'ribed several.

one half of the bight of the 'U formed of one material;

and the other arm and the other half of said bight of said U formed of a different material, means for integrally uniting said materials at substantially the center of said bight'to define a junction, said-materials being such that uponthe application of heat to said junction a potential will 'appear'acrossthe arms-ofsaid U, and means defin-' ing a restricted cross section'in said element.

2. In apparatus for converting heat directly to elec tricity, a stack of laminations, each lamination formed in somewhat of a U-shaped configuration with one arm andone half of the bight-of the U formed of onematerial,

for insulating adjacent laminations from each other, means. for. securing said lamination with interposed inof saidlaminations insaid'stack.

3. In apparatus for. converting heat. directly to electric" energy, a stack...of. laminations,..each lamination formed in somewhat of a. U.-shaped configuration with one arm andonehalf of vthebight of the .U formed of one mate{ rial, and :the other arm and the other half of the bight of said. U formed of a. different material, means for integrally. .uniting. said materials at substantially the center of said bight to define a junction, said materials being such that .upon .theapplicationof heat to said junction a potentialwill appear acrossthe arms .of each U, insulating means for insulating adjacent laminations from -each;.other,;means for;securing.said laminations with interposed-insulating means into a.- rigid' assembly, means forconnecting said laminations'in a series electrical cir-.-; I cuit, an elongated tube disposed between the arms of said U,.a pluralitybf orifices in-said tube directed toward said.

junctions,,andv meansfor supplying acombustible material to. said tube wherebysaid junctions are simultaneously heated.

References Cited in the file of this patent v UNITED STATES PATENTS 764,175. Bristol July 5, 1904. 764,177 f Bristol July 5, 1904 779,090 Marsh Jan. 3, 1905' 1,120,781 Altenkirch et a1. Dec. 15, 1914 1,677,029 Fuller July 10,1928 2,337,000: Ray Dec. 14, 1943 2,378,804 Sparrow et al June 19, 1945 2,502,399 Greefi Mar. 28, 1950 2,588,508 Findley Mar. 11, 1952* FOREIGN PATENTS 23,865 r Great Britain" of 1896. 73,936-- Austria Oct. 25, 1917 329,545 Germany Nov. 24, 1920 251,230 Great Britain Dec. 9, 1925- OTHER- REFERENCES Telkes, Mi: .The Eificiency of Thermoelectric Gener ators, Journal of Applied Physics, vol. 18, No. 6-, Decem-' ber 1947, pages ll161127.

The Thermodynamics of Physics and Matter, Prince-4.:

ton University Press, vol. I, page 618.

Born, Ml: Atomic Physics, page 264.

sulating. means into .a rigid assembly, means for connect-.- ingsaid laminations'in a series electrical .circuit, and. means .for.. simultaneously heating said. junctions .of each. i 

